St Mary's is a magnificent mid-14thc. church with an aisled and clerestoreyed nave of four bays, the E bay of each arcade giving onto transepts. A strainer arch of c.1400 crosses the nave a bay to the E of the chancel arch. The chancel has a N vestry, and to the S the easternmost side window has been blocked, apparently to strengthen the wall when the Dolben vault was built beneath the E end c.1710. The W tower is contemporary with the rest, although the parapet must be 15thc. It is topped by an ashlar spire with two rows of lucarnes. The spire was struck by lightning in 1897 and the top 30 feet of it rebuilt. The nave has N and S doorways, the S under a two-storey porch. The upper chamber is accessible through a turret added in 1794, and is known as the Monk's Cell. The only Romanesque work here is the font.

In 1086 Finedon was a large royal manor, previously held in dower by Queen Edith. There is no notice of the church until the 13thc., when the advowson of the rectory was in royal hands .

RCHME suggests that the church was rebuilt c.1320 on the foundations of a 12thc. cruciform building. This would explain the long transepts and unusual size of the church, comparable with Rothwell, Oundle and Raunds. The damage to the font is regrettable in view of the Christological cycle it appears to depict.